Fluid decontamination system

ABSTRACT

An apparatus and process for removing corrosive contaminants from a hydrocarbon including the steps of mixing water with a hydrocarbon contaminated with corrosive ions into a mixture and conducting the flow of the mixture tangentially relative to a surface of a plurality of microporous hydrophobic hollow fiber membranes and separating a permeate flow of decontaminated hydrocarbon from retentate mixture. An apparatus (10) is provided for this separation process which includes a mechanism for removing resistance to flow through the hollow fiber membrane (16) aiding in increased uniform tangential flow through the membrane (16).

This is a division of application Ser. No. 169,981, filed on Mar. 18,1988, now U.S. Pat. No. 4,790,941.

TECHNICAL FIELD

The present invention relates to a process and apparatus for movingcorrosive contaminants from fuels.

BACKGROUND OF THE INVENTION

The presence of sodium, sulfur, and other corrosive contaminants infuels burned in turbine, as well as reciprocating engines, causesexpensive maintenance problems and shortens engine life. Turbine enginefuel contamination problems are found in land and marine equipment,especially in middle east installations. Significant problems fromcontaminated fuel are also seen with turbine engines used for propulsionof ships. Fuel contamination results in corrosion of turbine engineparts, especially at high operating temperatures. High temperaturecorrosion results from the presence of vanadium, sodium and potassium.These elements form compounds during engine operation which formdeposits on components, dissolve coatings, and leave parts open tosulfidation attack.

Generally, refiners of hydrocarbon fuels employ processes to removesulfur and metal ion contamination from middle distillate hydrocarbonswhich are essentially procedures where the hydrocarbon is first treatedwith water (steam). Water is employed to extract water solublecontaminants from the hydrocarbons. Water, along with contaminants, isthen removed by using centrifugal methods, water coalescing techniques,passive gravity (settling) methods, and filtration. There are inherentinefficiencies in these multiple steps and reduction of water, sulfurand metallic contamination to levels that meet standards andspecifications of fuel users is often difficult and expensive.

Once purified at the refinery, middle distillate hydrocarbons oftenbecome recontaminated enroute to the point of use. Salty or contaminatedwater is often co-mingled with middle distillate fuels duringtransportation and storage. Users of middle distillate fuels, such asthose operating turbine engines, must maintain special fuel treatmentand purification equipment to protect their engines from damage. Mostturbine engine manufacturers specify liquid fuel purity requirements.Turbine engine fuels such as liquid petroleum gas, light virgin naptha,heavy virgin naptha, kerosenes, diesel fuels and gas oils are requiredto contain less than 1% by weight free water and less than 0.1parts/million of vanadium, sodium, potassium, calcium and lead. Coppermust be below 0.02 parts/million. Consequently, these engine fuels mustundergo purification processes that assure users that damage to internalcritical engine parts is minimized.

Prior art decontamination techniques often include multiple steps forthe purification of middle distillate fuels both at the refining stageand at point of use. These prior art techniques such as centrifugalmethods, coalescing processes, passive gravity settling and filtrationdo not always efficiently separate water and contamination from thehydrocarbon. A particularly difficult separation problem results fromthe oil/water interface between the water hydrocarbon phases.Centrifugal and passive gravity settling techniques cannot efficientlydeal with this interface and some cross-contamination frequently occursbetween the water and oil phases. Coalescers can handle only certainmaximum water volumes in petroleum hydrocarbons before they becomeoverpowered by entrained water and fail. Conventional filtration, ofcourse, is not capable of separation of water from hydrocarbons at all.

The present invention provides a simple, efficient technique whereinwater from any source is co-mingled with hydrocarbons, eitherintentionally or inadvertently and can be removed from the hydrocarbonswith a hollow fiber cross flow membrane system.

The former cross flow systems using hollow fiber membranes required apump which acted against fluid resistances generated by the pipingbetween the pump outlet and the entry to the separation module includingthe hollow fiber membrane. Loss of fluid from inside to outside of thehollow fibers, such as by permeation, causes a reduction in volume andresistance that is counter balanced by the resistance subsequentlygenerated by the hollow fibers themselves and by the piping during thereturn of the retentate fluid back to the reservoir of the system.

Contaminated fluid would be fed by a pump to a membrane cross separationmodel. Permeate would be conducted to an engine or a reservoir andretentate would be recycled back to a open reservoir. The reservoirwould be drained of settled contaminants. The reservoir would feed intothe contaminated fluid line being pumped directly to the membrane crossseparation module for recycling and further decontamination.

A further disadvantage of this system is the use of the reservoir. Adetection system must be employed with a reservoir in a cross flowsystem, such as float valves, for monitoring high and low fluid levels.This is required so that small changes in flow either to the system orout of the system do not cause the reservoir to either over flow orcause the pump to run dry. This necessary feature adds to the cost andreduces the reliability of the overall system. Further, as water buildsin the reservoir, a proportionate reduction in permeate flow rate occursunless this water is removed from the system. In many cases, the volumeof water is not large enough per unit volume of fluid beingdecontaminated, but there are occasions when the large water volume canenter the system and cause a significant permeate flow rate reduction.This represents a problem if the system is hooked directly to a jetengine fuel supply.

Another disadvantage of the use of reservoir in cross flow separationsystems is the inconvenience of removal of water and particulatecontamination in a continuous manner as it builds up in the retentatefluid during operation.

The present invention provides a decontamination system which furthereliminates the reservoir entirely and incorporates significantimprovements in system efficiency.

Inherent in the reservoir type systems is an inefficient use of theentire length of the hollow fiber membranes. Applicant has found thatthe portion of the hollow fibers proximate to the separation moduleinlet of the system meet a higher pressure head then those portions atthe distal end of the housing fibers proximate to the separation moduleoutput. The present invention further provides means for increasing theefficiency of the entire length of the hollow fiber membrane therebyincreasing the permeate output of a separation module unit.

SUMMARY OF THE INVENTION AND ADVANTAGES

In accordance with the subject invention there is provided a process formoving corrosive contaminants from fuels, the process including thesteps of mixing water with a hydrocarbon contaminated with corrosiveions into a mixture and conducting a flow of the mixture tangentiallyrelative to a surface of a plurality of microporous hydrophobic hollowfiber membranes and separating a permeate flow of decontaminatedhydrocarbon from the retentate mixture.

The present invention further provides a fluid separation apparatusincluding pumping means for pumping mixture from a source to a separatormeans and tangential flow separator means in fluid communication of thepumping means for separating by cross flow separation a fluid permeatefrom a fluid mixture retentate. The separator means includes an inherentresistance to uniform tangential flow. The apparatus includes resistanceremoving means for moving the resistance to flow through the separatormeans aiding in increased uniform tangential flow through the separatormeans.

DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated asthe same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 is a schematic diagram of a fuel decontamination systemconstructed in accordance with the present invention;

FIG. 2 is a second embodiment of the fuel decontamination system;

FIG. 3 is a perspective view partially broken away of a filter assemblyconstructed in accordance with the present invention; and

FIG. 4 is a fragmentary cross sectional view of a hollow fiber membraneillustrating tangential flow separation.

DETAILED DESCRIPTION OF THE DRAWINGS

A schematic representation of fluid decontamination apparatus isgenerally shown at 10 in FIG. 1.

Generally, the apparatus 10 includes a pump 12 for pumping a fluidmixture from a source 14 to a separator module 16. The separator module16 provides tangential flow separator means in fluid communication withthe pump 12 for separating by cross flow separation a flow ofdecontaminated hydrocarbon from the permeate retentate mixture, theseparator means 16 including an inherent resistance to uniformtangential flow. The apparatus includes resistance removing means forremoving the resistance to flow through the separator means 16 aiding inincreased uniform tangential flow through the separator means 16.

More specifically, the apparatus schematically shown in FIG. 1 at 10includes a source for contaminated fluid in fluid communication througha strainer 15 to a check valve 18 by means of conduit 20. The checkvalve 18 is in fluid communication to the pump through inlet conduit 22.Outlet conduit 24 is in fluid communication between the pump 12 andseparation module 16. Outlet conduits 26 and 28 carry a fluid permeateseparated from the contaminated fluid to a permeate destination 30, suchas a storage tank or directly to an engine for use. Outlet conduit 32carries fluid retentate from the separation module to be recirculated ininlet line 22.

The separator module 16 comprises a plurality of hollow fiber membranes34, shown in FIGS. 3 and 4. The membranes 34 are contained within aplastic web 36, the web being contained within a separator module 38.The separator module 38 includes an inlet 40 and a first pair of outlets42, 44 which are in fluid communication with conduits 26, 28respectively and a retentate fluid outlet 46 in fluid communication withoutlet conduit 32. The separator module 38 contains a plurality ofhollow hydrophobic microporous membrane fibers 40 contained as a bundlewithin the web 36. The fibers 34 are embedded in a potting material 48adjacent the inlet 40. Each fiber 34 includes a hollow core 50, thefiber 34 having an inner surface 52 extending about the hollow core 50.Each fiber 34 also includes an outer surface 54. The hollow cores 50 ofthe fibers 34 define a plurality of bores in fluid communication betweenthe inlet 40 and the outlet 46. The outer surfaces 54 of the fibers 34in combination with the inner wall of the module housing 38 define anouter chamber in fluid communication with the outlets 42, 44.

The membrane fibers 34 are microporous membranes separating the innerbores 52 from the outer chamber. The membrane fibers 34 extend parallelto the first flow path 56 and tangentially contact the length of theflow path 56.

The fiber 34 can comprise a homogeneous layer of microporous materialmade from hydrophobic materials such as polypropylene andtetraflurorethylene fluorocarbon resins. The resins included in thisgroup must be extremely resistant to degradation in the presentedenvironment of hydrophilic elements such as water and dissolved watersoluble components, as well as in the hydrocarbon environmental of thefluids.

For example, a ten inch module can contain 197 hollow fibers having ainner diameter of 0.6 mm and an average bore size of 0.20 microns. A 20inch module can contain 440 hollow fibers having an inner diameter of0.6 mm and an average bore size 0.20 microns. All values are plus minus10%.

As discussed in detail in the prior art section, prior art systemsincluding modules such as the module 16 of the present invention includeinherent inefficiencies in the separation process. The present inventionincludes resistance removing means for removing the resistance to fluidthrough the separator means 16 aiding in the increased uniformtangential flow through the separator means 16 and specifically throughthe fibers 34 thereby overcoming the inherent problems of prior artsystems.

The resistance removing means includes means for actively drawingretentate from the retentate outlet 46. By actively drawing theretentate from outlet 46, a positive decrease of the resistance normallyapplied by the inner surfaces 50 of the fibers 34 is effected.Accordingly, increased separation efficiency is obtained along thelength of the fibers 34 thereby increasing the efficiency of theseparation. In accordance with the subject invention, each fiber willseparate an increased amount of permeate from a unit volume of flow intothe separation modules over a given unit of time.

As shown in FIG. 1, the drawing means include the first conduit 20 influid communication between the contaminated fluid source 14 and thepump 12 and the second conduit 32 in fluid communication between theseparator module outlet 46 and the first conduit 20 whereby the pump 12simultaneously draws fluid mixture from the source 14 and retentate fromthe separator module 16, both fluids being mixed in the conduit 22 anddelivered through conduit 24 to the inlet 40 of the separation module16. The pump 12 actively draws contaminated fluid from the source 14while simultaneously the pump 12 draws retentate from the retentateoutlet 46 thereby counteracting against the resistance to flow throughthe separator means 16 and specifically through the bores 50 of thefibers 34 aiding in increased tangential flow trough the length of thefibers 34.

A second embodiment of the inventive resistance removing means in shownin FIG. 2. Like primed numbers are used to designate similar features ofthe two embodiments.

The drawing means includes the first conduit 24' in fluid communicationbetween the pump 12' and the inlet 40' of the separation module 16'. Asecond conduit 58 is in direct communication between the retentateoutlet 46' of the separation module 16' and first conduit 24' at an armof a venturi inlet, schematically shown at 60, thereby creating aventuri effect at the point of communication between the first andsecond conduits 24', 58 actively drawing retentate flow from theretentate outlet 46'.

This embodiment is particularly useful environments wherein an add-onpump to a system is not available. This system can be utilized ondevices such as gas pumps utilizing the pump already contained withinthe gas pump, the venturi effect acting as the drawing means. Theinvention would be useful at gas stations, airports, or boat docks,wherein the embodiment as shown in FIG. 2 could be added onto or splicedinto existing fuel delivery lines.

Referring to FIG. 1, the apparatus includes a third conduit 62 in fluidcommunication between the conduit 24 and the conduit 22 between thepoint of communication with the conduit 20 and the pump 12. A means fordehydrating fluid within the conduit 62 dehydrates the fluid mixtureflow passing therethrough. The dehydrating means can include a coalescer64 on-line with the conduit 62 for removing water from the retentateflow. The coalescer is an off line from the conduits deliveringcontaminated fluid from the source 14 through the pump 12 and to theseparation module 16 thereby not contributing to the fluid dynamics ofthe main line path of fluid flow through the system. However, thecoalescer 64 is capable through the alternate flow-through conduit 62 toefficiently remove water from the retentate flow at a rate independentof the fluid flow rate through the separation module 16.

The present invention further provides a process for removing corrosivecontaminants from fuels. The process includes the steps of mixing waterwith a hydrocarbon contaminated with corrosive ions into a mixture andconducting a fluid of the mixture tangentially relative to the surfaceof a plurality of microporous hydrophobic hollow fiber membranes andseparating a permeate flow of decontaminated hydrocarbon from theretentate mixture. The process is capable of separating contaminatesfrom the group including sodium, sulfur, potassium, calcium, lead andcopper from the hydrocarbon as the hydrocarbon tangentially flowsthrough the membranes.

More specifically, the inventive process utilizes the apparatusdiscussed above for recirculating the retentate through the membranefibers 34 to further remove decontaminated hydrocarbon permeatetherefrom. The hydrocarbon-water mixture is first made, intentionally orinadvertently, and the mixture is pumped from the source 14 to the inlet40 of the separation module 16 containing the microporous membranefibers 34 and through the bores 50 of the membrane fibers 34. The pump12 or venturi effect at 60 removes resistance of flow through the bores50 of the membrane fibers 16 aiding in increasing the uniform flowthroughout the length of the bores 50 of the membrane fibers 34. Theprocess thereby includes the step of removing resistance by activitydrawing retentate from the module outlet 46. Thusly, the resistance isremoved by mixing the retentate with the mixture from the source 14 andpumping the retentate and mixture from the source 14 to the inlet 40 ofthe module 16 and pumping the retentate from the module outlet 46 andrecirculating the retentate mixture back to the module inlet 40.Alternatively, the pump 12 is operatively connected to the module asshown in FIG. 2 and the retentate is conducted to the conduit 22'upstream of the pump 12' and the retentate is drawn into the conduit 22'by a venturi effect.

The process further includes steps of dividing a portion of the flow ofthe mixture from the pump 12 and dehydrating the divided portion of theflow and returning the dehydrated portion to the flow of mixture flowingto the inlet 40 of the module 16, as by use of coalescer 64.

The present invention is a simpler, more efficient technique than priorart methods of centrifugally removing contaminants from hydrocarbons.The present invention rapidly removes the contamination of hydrocarbonsutilizing hollow fiber cross flow membrane techniques. Further,corrosive contaminants are removed along with the water from thehydrocarbon. The hollow fiber member system is capable of removingsubstantially all of the free water (entrained water) from thehydrocarbons and it is also capable of removing dissolved (equilibriumvs. temperature dependent) water from the same hydrocarbons.

The present invention eliminates the necessity of the reservoir of priorart assemblies entirely and incorporates the recirculating system andcheck valve 18 of the present invention. The arrangement removes theresistance that formerly resulted from the pressure generated by thereturn line to the reservoir in the old systems.

This invention has been characterized as a push pull arrangement wherefluid is pumped into the separation module 16, and then pulled out andaway from the module 16 by having the retentate return flow directlyback to the suction side of the pump 12 or to the venturi as shown inFIG. 2. This arrangement has been discovered to be of particularimportance for the achievement of maximum fluid mechanical advantage ofany cross flow separation system.

The check valve 18 is important to the system as it regulates flow inthe retentate recirculation loop with flow coming from the incomingprimary contaminated fluid source 14. Check valve 18 also prevents flowof retentate backwards through the primary contaminated fluid feed line20. The retentate recirculation volume is therefore held to a minimumnot requiring a reservoir.

The strainer 15 removes particulate contaminants possibly containedwithin the original source 14 of fluid.

The present invention provides for efficient and continuous removal fromthe retentate main fluid volume without loss permeate flow rate. Thiseffect is seen even when 50% or more water is allowed to enter theprimary contaminated fluid feed stream. Water is quickly isolated by theside stream through conduit 62 and does not remain in the modulecirculation. Water particulate matter are thus trapped by the filterseparator for convenient disposal.

A further discovery utilizing the present invention is that the pressureexerted by the pump 12 upon the fluid passing through the inside of thehollow fibers 34 can be balanced with the permeate fluid pressure toachieve optimum permeate flow rate as well as optimum separationefficiency. Depending upon the viscosity of the fluid beingdecontaminated, temperature, and the diameter of the hollow fibers inthe separation module, the pump can be adjusted so as to achieve optimumretentate fluid flow velocity and pressure. The pump 12 not only pushesfluid to the module 16 but also serves to remove resistance to flowutilizing the push pull effect through the bores 50 of the fibers 34which significantly aids in maintaining truly tangential fluid flow.This effect dramatically improves the working surface area of the hollowfibers 34 within the separation module 16.

For example, in prior art systems, permeation begins to occurimmediately within the upper region of the separation module and fallsoff to nil to the extreme of the lower end of the module when the moduleis viewed in a vertical position. The same effect occurs when the moduleis in a horizontal position. This permeate flow reduction effect is morepronounced with high viscosity fluids but is also readily observablewith low viscosity fluids such as kerosene. The reason for this effectis that fluid resistance builds as the fluid from the retentate sideflows through the bores of the membranes. At the same time, fluid lossoccurs by permeation of fluid through the pores of the membrane 34. Thefluid loss is replaced by the fluid volume supplied by the pump and abalance is struck between contaminated fluid entering the system andpure permeate leaving the system. With prior art systems, the majorvolume of permeate is observed to occur only in the first half of themodule because the region near the outlet of the module exerts a highenough resistance to retard flow. This so called back pressure causespartial loss of tangential flow on the retentate side and causes thefluid to be forced to the pores of the membrane along with water andparticulate matter.

The present invention removes this resistance by directing the retentateflow on the module directly back to the pump suction inlet. In thismanner, build up of back pressure is eliminated in the module retentateside and true tangential flow is maintained regardless of the fluidviscosity. Optimum cross flow separation efficiency versus permeate flowrate are therefore achieved.

Referring to FIG. 1, the apparatus includes conduit 63 in fluidcommunication between conduit 24 and a three way valve 65. The three wayvalve 65 is in fluid communication with conduit 22 through conduit 66.The three way valve is in fluid communication with one side of a pistoncylinder assembly 68 through conduit 70. The functionally opposite sideof the piston cylinder assembly 68 is in fluid communication withconduit 26 through conduit 72. The combination of the three way valve65, cylinder assembly 68 and conduits 63, 66, 70 and 72 provide a backpulse membrane cleaning mechanism for the separation module. The systemeffectively removes debris from the fiber inner surfaces 52 of thehollow fibers 34 by creating a back pulse of fluid flow as retentateflow is maintained through the bores 50 of the fiber.

During start up or shut down, the three way valve 65 is adjusted toallow flow from conduit 63 through conduit 70 to force a piston 74within the cylinder 68 to move fluid in conduit 72 through conduits 26and 28 to create a back pressure from the outer surfaces 54 of thehollow fibers 34 through the inner surfaces 52 as a retentate flow ispassed through the bores 50 or the fibers 34. This pulse releases anyparticulate contamination of the inner surface 52 of the fibers 34. Allthat is necessary is a momentary back pulse to drive a volume of fluidbackward through the pores of the fibers 34 to release the particulatematter from the inner surfaces 52 as the retentate flow 56 sweeps theparticulate matter from the bores 50.

EXAMPLES

A contaminated fluid source of a unit constructed in accordance with thepresent invention was filled with three gallons of clear diesel fuel andcirculated through the system. Samples were taken from the reservoir andfrom the permeate outlet following this recirculation. These sampleswere marked "undoped fuel from tank or outlet". This system was thendoped with 500 ml of synthetic sea water, the fuel recirculated for fiveminutes and samples taken again from the reservoir tank and from thepermeate outlet. The results were as follows:

    ______________________________________                                                            SODIUM vppm                                               ______________________________________                                        Undoped Fuel from Tank                                                                              1.0                                                     Undoped Fuel from Permeate Outlet                                                                   0.1                                                     Doped Fuel from Tank  10                                                      Doped Fuel from Permeate Outlet                                                                     0.1                                                     ______________________________________                                    

It can be seen from the data obtained that the unit has a very highefficiency for water and sodium removal. This ability would be extremelyuseful in areas such as the Middle East where fuel supplies are veryvariable and also in marine and off shore uses where contact arisesbetween fuel and sea water.

The values obtained in the experiment are well within the guidelines setforth for industrial requirements of sodium and water removal from fuel.Unlike prior art units which would require centrifugation or a settlingstep, the present invention provides for immediate separationimmediately after the mixing of water and fuel. Hence, the presentinvention provides an extremely effective means for removing corrosivecontaminants from hydrocarbons, providing a time efficient means forobtaining these results.

The invention has been described in an illustrative manner, and it is tobe understood that the terminology which has been used is intended to bein the nature of words of description rather than of limitation.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the appended claims whereinreference numerals are merely for convenience and are not to be in anyway limiting, the invention may be practiced otherwise than asspecifically described.

What is claimed is:
 1. An apparatus for fluid separation comprising:pumping means (12) for pumping a fluid mixture from a source (14) to aseparator means; tangential flow separation means in fluid communicationwith said pumping means (12) for separating by cross flow separation afluid permeate from a fluid mixture retentate, said separator means (16)including a plurality of hollow fibers having an inherent resistance touniform tangential flow throughout the length of said fibers; andresistance removing means for removing said resistance to flow throughsaid separator means (16) including means for aiding in increasinguniform tangential flow through the entire length of said fibers of saidseparator means.
 2. An apparatus as set forth in claim 1 furthercharacterized said separator means (16) comprising said plurality ofhollow fiber membranes (34) including an outer surface (54) and an innersurface (52) defining bores (50), said membranes (34) being containedwithin a module (38) including an inlet (45), a permeate outlet (42, 44)in fluid communicate with said outer surfaces (54) of said membranes anda retentate outlet (46) in fluid communication with said bores (50),said resistance removing means including drawing means for activitydrawing retentate from said retentate outlet (46).
 3. An apparatus asset forth in claim 2 further characterized by including a first conduit(24') in fluid communicate between said pumping means (12') and saidinlet (40) and a second conduit (58) in direct communication betweensaid retentate outlet (46') and said first conduit (24') creating aventuri effect at the point of communication between said first andsecond conduit (24', 58) activity drawing retentate flow from saidretentate outlet (46').
 4. An apparatus as set forth in claim 2 furthercharacterized by said drawing means including a first conduit (20) influid communication between a fluid mixture source (14) and said pumpingmeans (12) and a second conduit (32) in fluid communication between saidseparator means (16) and said first conduit whereby said pumping means(12) simultaneously draws the fluid mixture from the source (14) andretentate from said separator means (16) into said first conduit.
 5. Anapparatus as set forth in claim 4 further characterized by including aone way check valve (18) on said first conduit (20) before the point ofcommunication between said first and second conduits (20, 22).
 6. Anapparatus as set forth in claim 5 further including a third conduit (24)in fluid communication between said pumping means (12) and said inlet(40) and a fourth conduit (62) in fluid communication between said thirdconduit (24) and said first conduit (22) between the point ofcommunication with said second conduit (22) and said pumping means (12),said apparatus (10) including dehydrating means in fluid communicationwith said fourth conduit (62) for dehydrating the fluid mixture flow. 7.An apparatus as set forth in claim 6 further characterized by saiddehydrating means including a coalescer (64).